OFFSET
0,3
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 566
FORMULA
E.g.f.: (-1+x)^2/(1-3*x+x^3)
Recurrence: {a(1)=1, a(0)=1, a(2)=8, (n^3+6*n^2+11*n+6)*a(n) +(-3*n-9)*a(n+2) +a(n+3)=0}
Sum(-1/9*(-1+2*_alpha^2-2*_alpha)*_alpha^(-1-n), _alpha=RootOf(1-3*_Z+_Z^3))*n!
a(n) = n!*A052545(n). - R. J. Mathar, Jun 03 2022
MAPLE
spec := [S, {S=Sequence(Prod(Z, Sequence(Z), Union(Z, Sequence(Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved